Telephone call transmitting device



May 14, 1946. F. A. HUBBARD TELEPHONE CALL TRANSMITTING DEVICE 2 Sheets-Sheet 1 Filed June 25, 1945 INVE/Vi'O/P F. A. 10,95,490 4. 7?

ATTORNEY Patented May 14, 1946 TELEPHONE CALL TRANSMITTING DEVICE Francis A. Hubbard, Maplewood, N. J., assignor to Bell Telephone Laboratories, Incorporated, New

York, N. Y., a corporation of New York Application June 23, 1943, Serial No. 491,959

This invention relates to telephone call trans- 5 Claims.

mitting devices used in telephone systems of the type in which the establishment of telephone connections between calling and called stations is controlled from the calling station by means of manually operable keys.

Key calling telephone systems have been devised heretofore which provide facilities whereby a telephone subscriber may selectively establish direct connections to any of a plurality of frequently called stations without resorting to the use of the regular telephone dial, or relying upon binations, depending upon the character of the I impulse combination transmitted from the calling station, to selectively control the operation of called station-connecting switching devices. A particular system of this type is disclosed in Patent No. 2,364,771, issued December 12, 1944, to Henry M. Bascom and Francis A. Hubbard, and is characterized by the use of a key-set whose keys function during both their downstrokes and their upstrokes to transmit complete station identifying signals of the two-interval type. The utilization of both strokes of a station selecting key in this system obviates the need for a ground connection at the subscribers station and renders it possible to transmit fifteen different station selecting signals over the metallic loop which comprises the subscribers substation circuit, the

signal receiving circuit and the two interconnectin-g line conductors.

It is the object of this invention to simplify and otherwise improve key calling telephone systems of the general type disclosed in the above-identified patent.

This object is attained in accordance with a feature of the invention by the use of a fourbutton key-set whose keys are actuated twice or in various combinations of two keys consecutively, each combination of two key operations controlling the selection of a different called subscribers line. This feature results in a simplification of the subscribers telephone set and renders it possible to effect fifteen different station selections with but four keys. The key-set of this invention controls a simplifled signal receiving circuit whose signal receiving relays function on a release basis to control the selective operation of the register relays of the register circuit. More particularly, the signal responsive relays are all operated in response to the initiation of a call at a subscribers station and prior to the actuation of the station selecting keys, and are then selectively released singly or in combinations in accordance with the actuation of the particular keys.

In the present system, the station selecting codes are based on polar-marginal combinations whereby both positive and negative half cycles may function at either of two magnitudes. The positive and negative characteristics of the signal impulses are determined by a pair of oppositely poled dry rectifiers which may be separately connected to the signaling circuit under the action of individual keys, and the marginal characteristic is obtained by effectively including in or excluding from the circuit with either of the dry rectifiers a resistance element. A further feature of the invention, accordingly, resides in a particular design of a four-button key-set having but three spring pile-ups, one of which is associated with each of the dry rectifiers and the third of which controls the resistance element, and in so constructing the key-set that each of the rectifier controlling spring pile-ups may be separately operated by its own individual key, or each may be operated simultaneously with the resistance controlling spring pile-up by a particular one of the two remaining keys of the fourbutton key-set.

These and other features of the invention will be readily understood from the following detailed description when read in connection with the accompanying drawings in which:

Fig. 1 is a circuit diagram disclosing a fifteenstation key calling system embodying features of the invention;

Fig. 2 is a front view of a four-button telephone subscribers set with the front face thereof broken ister magnets operated and the lines selected for each of the fifteen different combinations of two keys in which the four keys are operable.

Reference will. now be made particularly to Figs. 2 and 3 which show the four-button key-set of this invention mounted in the base of a telephone set housing I00. The key-set itself consists of two horizontal mounting plates It and I02 which are held in superposed spaced relation by means of the cylindrical members I03 which are tap d at either end to receive the screws I04. This framework is supported on the base I05 by means of two brackets I06 having flanges at either end which abut, respectively, the underside of the upper plate IM and the inner face of the base I05 and are fixed thereto by screws I01. Each of the plates IN and I02 is furnished with aligned holes, the two outer holes in the lower plate I02 being slightly larger in diameter than the two outer holes in the upper plate IN, and the two inner holes in the lower plate I02 being slightly smaller in diameter than the corresponding holes in the upper plate IOI The lower plate is provided with a fifth hole of substantially the same diameter as the two outer holes thereof and located midway between the two smaller holes. These holes accommodate the plungers which are controlled by the key buttons as will presently appear.

The two outer plungers I08 are identical in construction and each consists of a main body portion or shank tapered at one end and provided with an integral projection of smaller diameter at the other end which protrudes through its respective hole in the upper plate li. Each of the plungers I 08 carries a rectangular projecting arm I I0 which is rigidly fixed to its respective plunger in any convenient manner. The arm I I0 of the right-hand plunger I08 project's towards the left whereas the arm IIO of the left-hand plunger I08 projects to t,he right for a purpose to be explained presently. Each of the plungers I08 has its--upper end in cooperative engagement with a manually operable button.

The two inner plungers II2 are substantially identical in design and each consists of an intermediate portion of substantially the same diameter as the shanks of the plungers I08, an integral projection of smaller diameter extending from the upper end thereof and a longer integral portion of still smaller diameter extending from the lower end thereof. The left-hand plunger I I2 carries an arm I I4 which extends in either direction therefrom in such a manner that the lefthand portion thereof normally rests upon the arm I I0 of the left-hand plunger I08. The right-hand plunger II2 carries a substantially s-shaped arm whose right-hand portion normally rests upon the arm IIO of the right plunger I08 and whose lefthand portion is apertured to receive the upper end projection of a. short plunger H5. The plunger I I has its lower end tapered and is provided with an annular shoulder I I8 near its upper end which cooperates with the lower plate I02 to confine a coil spring I I! mounted on the shank of 55 equispaced integral depending arms I28 which, with the flared bushings I22, effect four compartment within each of which a plunger-actuating button is free to move. The buttons, designated I, 2, 3 and 4, respectively, are each provided with an integral centrally disposed projection at its lower end which is normally in contiguous association with the upper end of a plunger. Each button, near its lower end, is provided with a flange which serves to guide the button in its downward travel in its respective compartment.

The springs II8 normally maintain their respective plungers I08 in raised position, in which positions the shoulders of the shank portions thereof abut the under surface of the plate lot and the upper ends thereof, by virtue of their engagement with the buttons i and 8, respectively, maintain these buttons in the normal unactuated positions illustrated. The spring Ill serves the same purpose in connection with plungers IE2 which communicate with the under surfaces of the buttons 2 and 3.

The tapered end of the left-hand plunger itiii serves, when depressed, to actuate a spring pile-up comprising contacts a and A; the tapered end of the right-hand plunger I08 serves, when depressed, to actuate a spring pile-up comprising contacts?) and B; and the short center plunger H5 serves, when depressed, to actuate a spring pile-up comprising the contacts C.

When the key button I is depressed, the associated plunger I08 moves downwardly against the action of the corresponding spring I I8, disengages its arm I I0 from the left portion of arm H0 and causes the contacts a to be opened and the contacts A to close. Contacts A and a are of the make-before-break type so that the contacts A close before the contacts a open. Key button 8, when depressed, move its corresponding plunger I08 downwardly against the action of spring I I8, opens contacts b and closes contacts B. When key button 2 is actuated, the arm lid associated with the left-hand plunger I I2 acts upon both the left-hand arm H0 and the upper end of plunger I I5 whereupon both the left-hand plunger I08 and the plunger I I5 are depressed, the former to operate contacts a and A, as described above, and the latter to open contacts C. The key button 3, by virtue of the S-shaped arm-carried by the right-hand-plunger II2 with which the button 3 communicates,m0ves both the righbhand plungers I I2 and I08 downwardly, the former to open contacts C and the latter to open contacts b and to close contacts B. Contacts B and 17, like contacts A and a are of the make-before-break type. When the actuated buttons are released, the springs III and H8 operate in an obvious manner to restore the actuated plungers and their corresponding buttons to normal.

It is apparent from the above description that the spring pile-up consisting of contacts a and A responds to the depression of either of the buttons I and 2 and that when the button 2 is depressed the operation of the contacts a and A is accompanied by the operation of contacts 0. Similarly the spring pile-up consisting of contacts b and B responds to the depression of either of the buttons 2 and 3 and when the button 3 is depressed the operation of contacts b and B is accompanied by the operation of contacts C.

Mounted on the outer face of the telephone set housing I00 in back of the buttons are four designation holders I 25 each of which carries a numeral 1, 2, 3 or 4 in alignment with buttons correhousing of the telephone set is provided with five spondingly numbered in Fig. 2.

In Fig. 1 the key-set described aboe is schematically illustrated at the upper lei and the contacts of the three spring pile-ups indicated in Figs. 2 and 3 bear the same designations in Fig. 1. The subscribers telephone set has housed therein the dry rectiflers l and I2 and the resistance element l3 and these elements are\connegted to the contacts of the three spring pileps as shown in Fig. 1. The telephone equipment usually located at a subscriber's station is designated S and as illustrated is normally connected through the loop indicated by the broken lines to armatures of a cut-through relay II by way of the normal contacts a and b of the key-set KS, the back contacts of the said armatures being normally connected to the secondary winding of transformer whose primary winding is connected to the GO-cycle source of current P. When key button I is actuated, the contacts a are opened causin the disconnection of the subset S, and contacts A are closed to effectively connect the rectifier I0 across the link extending to the source P (assuming the receiver switchhook contacts at S are closed). This connection extends from the inner upper armature of relay l4, conductor l6, normally closed contact C of the key-set, rectifier it, closed contacts A of the key-set, normally closed contacts b of the key-set, conductor I I and the middle. lower armature of relay l4. When key button 2 is depressed, the connection efiected thereby extends from the inner upper armature of relay l4, conductor l6, resistance l3, rectifier it, closed contacts A, closed contacts b, conductor ill, to the middle lower armature of relay l4. When key button 3 is actuated, the connection effected extends from the inner upper armature of relay l4, conductor lb, resistance I3, rectifier it, closed contacts B, conductor ll to the middle lower armature of relay M. When key button 4 is actuated, the resulting connection extends from the inner upper armature of relay [4, conductor iii, closed contacts C of the key-set KS, rectifier it, closed contacts B, conductor ill to the middle lower armature of relay it. The key button 4, when actuated, also opens contacts b which disconnects the subset S from'the line. It is apparent from the foregoing that the rectifiers Ill and it may be selectively included directly in the signaling circuit separately by the actuation of key buttons I and 4, respectively, and each may also be included therein in series with resistance l3 by the operation of key buttons 2 and 3, respectively. Depending upon which of the rectifiers Ill or 12 is connected in circuit and upon whether or not the connection includes the resistance I3, the character of 'the signaling current is determined and may be either positive or negative half cycles of alternating current of either of two magnitudes.

The signal current receiving circuit includes three relays I8, is and 20. Relay I8 is a marginal two-winding relay having one winding connected in parallel with each of the windings of Relays l8, IS an 20 control the operation of relays 25, 28 and 21, which in turn, control the register circuit which includes relays I, 2, 4

and 8'. The armatures of register relays I, 2'

intended for the substation associated with line l I will be described in detail.

In practice the subscriber's station S would be provided with a card upon which wouldbe listed the names of the subscriber with whom direct connections may be established, and alongside each name would be indicated the combination of keys or buttons that must be actuated to effect a connection to the particular subscribers. As shown on the table of Fig. 4, the key I is actuated twice to effect a connection to line I I.

When the subscriber removes the handset from its support at station S and prior to the actuation of any key of the key-set KS both half waves of alternating current from source P fiow through the substation equipment in an obvious circuit which includes the normally closed contacts a and b of the key-set. Relays l8, l9 and 20 would accordingly operate since both half waves are transmitted and the resistance [3 is not included in the circuit. It will be observed that when both relays I9 and 20 are operated at the same time the operating circuit for relay 25 is opened and n signal is recorded. The signaling code is so devised that each station selection requires the transmission of two signal components, either of which may include one or the other polarity of the signaling current but not both polarities. The armatures and contacts of relay i9 and 20 are so interconnected that the simultaneous operation of both relays doesnot result in false signaling.

The subscriber next actuates the key button I twice in accordance with the instructions printed or otherwise displayed on the card located at the station S. When key l is actuated the contacts A are closed and contacts a opened. The latter disconnect the subset S and the former connect rectifier [0 in the signaling circuit. Rectifier I0 is so poled as to suppress the positive, half cycles and to permit the passage of the negative half cycles only. Thus the relays l8 and 20 hold operated while relay l9 releases. The circuit in which relay 20 holds operated extends from the lower terminal of transformer 15, winding of relay 20, rectiflers 24 and 2i, back contact and middle lower armature of relay l4, conductor l1, normal contacts b, closed contacts-A, rectifier [0, normal closed contacts C, conductor l6, inner upper armature and back contact of relay M, to the upper terminal of transformer IS. The right-hand winding of relay l8 being connected in parallel with the winding of relay 20 is also energized by the negative half cycles of current and remains operated. Thus the depression of key button I causes the suppression of the positive half cycles and the consequent release of relay l9 which operates only on the positive half cycles.

With relay l9released and relay 20 still operated, slow operating relay 25 operates in a circuit extending from grounded battery, armature and front contact of relay 20, back contact and righthand armature of relay I9, winding of relay 25 to ground. Relay 25, at its outer right armature and front contact establishes an obvious operating circuit for relay 21. At its inner left armature and front contact relay 25 completes a circuit extending from grounded battery, left armature and back contact of relay I9, inner left armature and front contact of relay 25, innermost left armature and back contact of relay 25, conductor 50 to ground through the winding of register relay I. When relay 2'! operated as mentioned above, it established'an obvious locking circuit for itself to battery 5| associated with the normal make-beforebreak contacts of relay I4, and at its outermost armature it furnishes locking battery for register relay I. This register relay accordingl is now operated and locked under control of relay 2! which, in turn, is locked operated under control of relay I4.

When the key I of key-set KS restores to normal the contacts A are opened and contacts a reclosed. The circuit is thus in the same condition'it was in prior to the actuation of key I in which both half waves of alternating current traverse the signaling circuit. Thus the positive half waves, being no longer suppressed, cause relay I9 to reoperate while relays I8 and remain operated. .The reoperation of relay I9 causes relay to restore its armatures. Relays 21 and I, however, remain operated, being locked as described above.

When relay 25 restores its outer right armature and with relay 21 locked operated, relay 26 operates in a circuit extending from grounded battery, outer right armature and back contact of relay 25, middle armature and front contact of relay 21, winding of relay 26 toground. Relay 26 in attracting its two inner left armatures transfers the armature contacts of relay 25 from the windings of register relays I and 2 to the windings of register relays 4' and 8' to prepare these relays to register the signal component .transmitted when the second key or button is actuated, or in the case being described, to register the signal component transmitted incident to the second operation of key button I. Relay 26 also looks to battery 5I.

When key button I is reactuated, the contacts A are again closed and contacts it opened. The positive half cycles of current from the source P are again suppressed due to the inclusion of the rectifier III in the signaling circuit, so that relay I9 again releases and relays I8 and 20 hold operated. Relay 25 accordingly reoperates. A circuit may now be traced from grounded battery, left armature and back contact of relay I9, inner left armature and front contact of relay 25, innermost left armature and front contact of relay 25, conductor 52, winding of register relay 4' to ground. Relay 4' locks to battery at the .outermost armature and front contact of relay 21, which relay 21, as above described, is locked operated to battery 5|.

When the operation of relay 25 was followed by the reoperation of relay 25 incident to the second operation of key button I of the key-set KS a circuit was established extending from grounded battery, inner right armature and front contact of relay 25, outermost left armature and front contact of relay 25, to ground through the upper winding of cut-through relay I4 which is slow-to-operate. Relay I4 operates in this circuit and in attracting its outermost lower armature transfers the battery 5| from the holding circuits for relays 28 and 21 to the holding circuits for register relays I 2', 4' and 8'. The

contacts controlled by the outermost lower armarelays are completed before the locking circuits for relays 25 and 21 are interrupted. Thus the operated register relays I and 4 are held operated when the original locking circuits therefor are opened by the release of outermost left armature of relay 2'3.

With register relays I and 4' and cut-through relay I4 operated, an energizing circuit for line connecting relay 3| is completed. This circuit extends from grounded battery, outer upper armature of relay I4, conductor 54, winding of relay 3|, conductor 65, back contact and third right armature of register relay 8, front contact and second right armature of register relay 4', back contact and first right armature of register relay 2', front contact and right armature of register relay I to ground. Relay 3|, in operating, connects the line II to the link L, which by way of the first upper and lower armatures of relay I4 and their associated front contacts, is connected to the line extending to the calling station S.

The register relays I and 4 which cause the operation of line connecting relay 3I are now held operated under the control of cut-through relay I4 which is now held operated under control of the subscriber's switchhook contacts. This holding circuit for relay I4 may be traced from grounded battery 55, conductor 55 of the link L, front contact and inner upper armature of relay I4, through the telephone circuit at station S, contacts a and b of the key-set KS, conductor I'I, lower winding of relay I4, conductor 51 of link L, to ground at 5B.

At..the back contact of the inner upper armature and the back contact of the middle lower armature of relay I4, the alternating current source P is disconnected from the line extending to station S and all relays, other than register relays I' and 4', line connecting relay 3|, and cut-through relay I4 are returned to their normal unoperated condition. At the termination of the call the telephone handset at station S is restored to its mounting thus causing the release of relay I4 which, in turn, causes register relays I and 4' and the line connecting relay 3| to be deenergized.

It is deemed unnecessary to trace through the operation of the circuits for each of the fifteen connections which may be completed by means of the key-set KS, since the table disclosed in Fig. 4 clearly indicates the key-set contacts operated for each key combination employed; the register relays which respond to such contact operations; and the line selected by the various combinations of register relays operated. It may be well, however; to briefly describe the circuit operationsinvolved in a connection which involves the contacts C of the key-set since such contact operation results in the release of marginal relay I8 of the signal receiving circuit. It will be assumed, therefore, that the subscriber at station S desires to communicate with the party whose station is located on the line 42 and, in accordance with the table of Fig. 4, first operates key 4 and then operates key 3 after having removed the handset from its support.

The operation of key 4 closes contacts B and 75. opens contacts b, the former connecting the rectifier I2 in the signaling circuit and the latter opening one side of the subscriber's substation circuit. As in the previously described case, relays It, IS and 20 operate when the handset is removed from its mountingat station S. When key 4 is depressed the contacts B connect the rectifier I2 in circuit, which rectifier is poled so as to suppress the'negative half cycles of current from the source P. With the negative half cycles suppressed, the positive half cycles traverse a path extending from the upper terminal of the secondary winding of transformer I5, back contact and inner upper armature of relay I4, conductor I8, normally closed contacts C of the key-set KS, rectifier I2, closed contacts B, conductor-i'l, middle lower armature and back contact of relay I4, rectifier 22, winding of relay I9, rectifier 23, to the lower terminal of the secondary winding of transformer I5. Relay I9 accordingly remains operated as does also marginal relay it whose left winding is connected in parallel with the winding of relay I9. Relay 20, however, releases due to the suppression of the negative half cycles.

Relay it: now operates in a circuit extending from grounded battery, back contact and armature of relay 20, front contact and right armature of relay I9, winding of relay 25 to ground. Relay it, operated, performs the same functions performed thereby in the previous description incident to the first operation of key I. Relay it operates and locks to battery 5|, and at its outermost armature and front contact supplies locking battery for the register relays I', 2, 4' and t. It will be observed that with both relays it and it in their operated condition the battery associated with their right and left armatures, respectively, is disconnected from the left arma- -tures of relay 25 so that neither of the register relays l and 2 finds an energizing circuit. Thus, no register relay functions incident to the depression of key 4. Relay 21 is held operated as described.

When the key 4 is released both half cycles of current are again free to traverse the signal receiving circuit and relays I8 and I9 remain operated and relay reoperates. Relay accordingly releases its armatures, causing relay 26 to operate in a circuit from grounded battery, outer right armature of relay 25, middle armature and front contact of relay 27, winding of relay '26 to round.

Relay it, at its right armature and front contact locks to battery 5i, and at its two inner left armatu'res transfers the left contacts of relay 25 from register relays i and 2 to register 'relays t and 3 whereby the latter two relays become available to register the signal component transmitted incident to the operation key 3 of the key-set.

The operation of key 3, as described earlier in the specification and as schematically shown in Fig. 1, causes contacts 0 to open, contacts 13 to close, and contacts b to open. Contacts b open one side of the subscribers subset connection, contacts B connect the rectifier I2 in the signal-- lng circuit, and contacts C remove the short from resistance I3. Thus the negative half cycles are suppressed and the positive half cycles continue to flow but at reduced magnitude due to the inclusion of the resistance I3 in the circuit. Relays IG and 20 accordingly release, the former due to the fact that the current value of the positive half cycles is reduced beyond that required to maintain the relay operated.

Relay 25 operates as before. A circuit may now be traced from grounded battery, armature and back contact of relay I8. outer left armature and front contact of relay 25, middle left armature and front contact of relay 26, conductor 60, winding of register relay 8' to ground. Relay 8 operates in this circuit and locks to battery at the outermost armature and front contact of relay 21. manner previously describedsand performs the same functions ascribedto it hereinbefore, which functions include the completion of a substitute locking circuit for register relay 8'.

With relays 8 and I4 operated, line connecting relay-45 operates in a circuit extending from grounded battery, outer upper armature of relay I4, conductor 54, winding of relay 45, outermost right front contact and armature of register relay '8', outermost right back contact and armature of register relay 4, outer right back contact and armature of register relay 2, back contact and right armature of register relay I to ground. Relay 45 connects the line .43 to the link L which, as a result of the operation of relay I4, is connected to the line extending to the calling station S. The remainder of the circuit operations are identical to those described in connection with the seizure of line I I. 7

If desirable, each of the buttons I, 2, 3 and 4 of the key-set may be provided with a separate sprin for maintaining it in its normal unoperated position, When such individual springs are provided the buttons I and 4 will remain in their normal positions where their respective plungei's I08 are depressed incident to the actua tion of buttons 2 and 3, respectively.

It is to be understood that no attempt has been made to illustrate instrumentalities which may be employed in signaling the called line or for tripping the ringing current incident to the response of the called party since such devices and their control are well known in the art and do not constitute a part ofthe present invention. It is also understood that the relay I4 may take other forms and may be included in the line circuit in a manner different from that illustrated where relatively lon line loops are encountered.

What is claimed is:

1. In a. signaling system in which a station desi'gnation is characterized by a two-interval code signal consisting of two distinct components, each of which may comprise positive half cycles of either of two intensities or negative half cycles of either of two intensities, the combination of a line, a source of alternating current, means for connecting said source to said line to cause said line to be traversed by positive and negative half cycles of a particular intensity, and a. designation transmitter comprising a plurality of manually operable keys, contact sets fewer in number than said keys, a rectifier connectable to said line by one of said contact sets, when operated, to suppress positive half cycles from said line, a rectifier connectable to said line by another of said contact sets, when operated, to suppress negative half cycles from said line, a resistance connectable in series with either of said rectifiers by a third of said contact sets to alter the intensity of the unsuppressed half cycles, an operating device for each of said first two contact sets, and a pair of operating devices for said third contact set, the operating device for each of said first two contact sets being mechanically coupled to a different one of the operating devices for said Cut-through relay I4 operates in the third contact set and each of said operating devices being operable by a different one of said keys.

tifying code signals are characterized by two sequentially transmitted signal components each comprising positive or negative half cycles of alternating current of either of two magnitudes, the combination of a station, a line extending therefrom, a source of alternating current associated with said line, and a signal transmitter at said station comprising a pair of oppositely poled rectifiers, a separate set of contact springs for controlling the connection of each or said rectiflers to said'line, a resistance, a single set of contact springs for effectively including said resistance in series with either of said rectifier-s, a manually operable key for each of said first sets of contact springs, and a pair of individually manually operable keys for said last set oi. contact springs, each key of said pair of keys being mechanically coupled to a different one of said first keys whereby the operation of either of said pair of keys results in the operation of said resistance controlling contact springs and also of a particular one of said rectifier controlling contact springs.

3. The combination in a signaling system of.

a line, a source of alternating current, a station on said line, means at said station for connecting said source of current to said line whereby both positive and negative halt cycles of alternating current from said source traverse said line at full intensity, means at said station for selectively suppressing the positive and negative halt cycles of said source and for altering the intensity of the unsuppressed half cycles comprising a first rectifier, a second rectifier, a resistance, a spring pile-up having a normally open contact connected to one terminal of one of said rectifiers, a spring pile-up having a normally open contact connected to one terminal of the other of said rectifiers, a spring pile-up having normally closed contacts each connected to a different terminal of said resistance, the other terminals of said rectifiers being permanently connected to one terminal of said resistance whose other terminal is connected to one of the conductors of said line and each of said first two spring pile-ups having a contact normally connected to the other conductor of said .line, means individual to each of said spring pile-ups for effecting their operation, a key for each of the operating means of said first two spring pile-ups, and a pair of individually operable keys for the operating means of said third spring pile-up, the operating means of each key of said pair of keys being mechanically coupled to the operating means or a diflerent one of said first two keys, whereby the operation or one of said pair of keys actuates the operating means 2. In a signaling system in which station idenotsaid third spring pile-up and also the operating means of one of said first spring pile-ups.

4. The combination in a code transmitter for use in a selective signaling system in which code signals are characterized by two signal components each consisting of either positive or nega-- tive half cycles of either of two intensities derived from an alternating current source, of means including a first set of contact springs for positively characterizing a signal component, means including a second set of contact springs for negatively characterizing a signal component, means including a third set of contact springs for determining the intensity oi. a signal component, a depressible operating device for each of said first two sets of contact springs, a pair of depressible operating devices for said third set of con tact springs, means mechanically coupling the operating devices of said first and second sets depression of either one of said pair of operating devices results in the simultaneous depression of the corresponding operating device oi said first or second set of contact springs and the depression of either of the operating devices of said first or second set of contact springs is ineffective to cause the depression of the corresponding one of said pair of operating devices, and manually operable means individual to each of said operating devices for causing the depression thereof.

5. A code transmitter of the push-button type for transmitting fifteen difl'erent two-component signals incident to the depression of any one button twice or of any two buttons successively, comprising only three sets of signal-characterizing contact springs, only four push buttons, an operating member for each set of contact springs, the operating member for each of a first two of said sets or contact springs being operable directly by a difierent one of said four buttons, a pair of depressible devices each operable directly by a diflerent one of the remaining two buttons, and means carried by each of said depressible devices for effectively coupling the operating member 01' the third set of contact springs and the operating member of a difierent one of the other set of contact springs, whereby the operation of either of said depressible devices by its corresponding button causes the simultaneous operation of an operating member of one of said first two sets of contact springs and the operating member of said third set of contact springs, and whereby the operation of a button corresponding to either of the operating members of said first two sets of contact springs causes only the operation of the said corresponding operating member and oi the set of contact springs corresponding thereto.

FRANCIS A. HUBBARD. 

